<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <!-- 某些结果是基于之前数据实时计算出来的，我们可以利用计算属性来完成 -->
        <ul>
            <li>西游记；价格：{{xyjPrice}}，数量：<input type="number" v-model="xyjNum"/></li>
            <li>水浒传；价格：{{shzPrice}}，数量：<input type="number" v-model="shzNum"/></li>
            <li>总价：{{totalPrice}}</li>
            {{msg}}
        </ul>
    </div>

    <script src="../node_modules/vue/dist/vue.js"></script>
    <script>
        // watch可以让我们监控一个值的变化，从而做出相应的反应
        new Vue({
            el: "#app",
            data: {
                xyjPrice: 99.98,
                shzPrice: 99.00,
                xyjNum:1,
                shzNum:1,
                msg:""
            },
            computed: {
                totalPrice() {
                    return this.xyjPrice * this.xyjNum + this.shzPrice * this.shzNum;
                }
            },
            watch: {
                xyjNum(newVal, oldVal) {
                    console.log("newVal==>", newVal, "oldVal==>", oldVal);
                    if (newVal > 3) {
                        this.msg = "库存超出限制";
                        // this.xyjNum = 3;
                    } else {
                        this.msg = "";
                    }
                }
            }
        });
    </script>
</body>
</html>